Surface transport systems have been proposed in which the vehicles or transport cars or transport dolleys are equipped with a vertically extending combination current pick-up and direction control rod to permit operation of the vehicle on floor surfaces, for example in warehouses, independently of tracks or the like laid into the floor of the warehouse. Rails or tracks laid into the floor of warehouses cause substantial costs, interfere with the smooth surface, and are sources of accidents. Further, it is difficult to change their position. It is, thus, desirable to provide load transport apparatus which can operate on a smooth surface. Internal combustion engines frequently cannot be used because of the resulting exhaust fumes; electric battery driven vehicles suffer the disadvantages of all battery energy supply: high cost, low efficiency, and limited range, coupled with a poor dead weight/load carrying ratio. Providing electrical energy by an overhead conductor, for example by a trolley wheel or slider from an overhead system, has the advantage that the transport apparatus can receive substantial power at minimum cost, operate at high efficiency, and yet be independent of any rail guidance since the connecting element, typically a rod or a tension cable, can be used simultaneously as a guide element for the vehicle. An overhead system is provided, located at a level of from between about 3 to 4 m (approximately 10-13 feet) above floor level, including electrical supply conductors and guide rails, which may be integrated with, or form part of an assembly of the supply conductors. The connecting element is coupled to a comparator, which may be located on the vehicle and which senses lateral deflection of the connecting element with respect to the position of the guide rail and/or electrical conductor mounted on the sealing. If such a deflection occurs, an error signal is generated which controls steered wheels or a steering wheel of the vehicle in a direction to null the transverse deflection, so as to place the vehicle precisely beneath the guide rail system. The steering control is simple--for example by a reversible electrical servo motor, receiving control signals via an amplifier from the deflection sensing element, so that deflection with respect to a reference is sensed.
The system has a substantial advantage: expensive and heavy batteries for drive of the vehicle are not needed, so that the vehicle can be operated essentially continuously, without down-time for recharging of batteries or replacement thereof by charged batteries. No installations in the floor surfaces in the form of guide cables and the like are needed, from which, for example, inductive signals could be picked up. The vehicle, thus, is cost-and energy-efficient and flexible.
Any automatic guidance system has an inherent disadvantage: The guidance along the directed path is determined by a mechanically installed element--a cable in the floor or, in an overhead system, the overhead current-and-guide rail arrangement. Changes in the guide path thus can be effected only by repositioning the respective guide elements. In case of an overhead system, it is necessary to disassemble the overhead electrical system from its support, reposition the system, and reassemble the system on a support, for example on transverse guide rods located in or on or beneath the ceiling of the respective warehouse or other installation. Change in the position of the guide path, thus, is comparatively expensive.